Polymers of carbon monoxide and olefins, such as ethylene, have been known and available in limited quantities for many years. For example, such polyketones are disclosed in Kirk-Othmer Encyclopedia of Chemical Technology, Second Edition, Vol. 12, p. 132, 1967, and in Encyclopedia of Polymer Science and Technology, 1968, Vol. 9, 397-402. It is known that polyketones are prepared by contacting CO and ethylene monomers in the presence of a catalyst. High molecular weight polymers of ethylene which contain small quantities of carbon monoxide can be prepared with the aid of Ziegler catalysts. Low molecular weight polymers of carbon monoxide with ethylene and possibly other olefinically unsaturated hydrocarbons in which all monomer units occur distributed at random within the polymer can be prepared with the aid of radical catalysts such as peroxides. A special class of the polymers of carbon monoxide with ethylene comprises the high molecular weight linear polymers in which the monomer units occur in alternating order, which polymers consist of units with the formula --CO--(C.sub.2 H.sub.4)--. Such polymers can be prepared with the aid of, among others, phosphorus-, arsenic-, antimony-, or cyanogen-containing compounds of palladium, cobalt or nickel as catalysts.
High molecular weight linear alternating polymers of carbon monoxide and ethylene consisting of units of the formula --CO--(C.sub.2 H.sub.4)--, can also be prepared by using catalyst compositions comprising:
(a) a compound of a Group VIII metal selected from the group consisting of palladium, cobalt and nickel,
(b) an anion of a non-hydrohalogenic acid having a pKa less than 6, and
(c) a bidentate ligand of the general formula ##STR1## wherein each M is phosphorus, arsenic or antimony, R is a bivalent organic bridging group containing at least two carbon atoms in the bridge and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 represent hydrocarbyl groups or substituted hydrocarbyl groups wherein the substituents are polar groups.
Polymerization employing these catalyst compositions of a monomer mixture which, in addition to carbon monoxide, comprises for example ethylene and a lesser amount of one or more alkenically unsaturated hydrocarbons having the general formula C.sub.x H.sub.y leads to the formation of polymers with units of the formula --CO--(C.sub.2 H.sub.4)-- and units of the general formula --CO--(C.sub.x H.sub.y)-- occurring randomly distributed throughout the polymer chains. The structures of the copolymers and terpolymers only differ in that in the case of the terpolymers a group --(C.sub.x H.sub.y)-- is encountered at random places in the polymer instead of a --(C.sub.2 H.sub.4)-- group.
The polymer preparation employing the above-described catalyst compositions has been carried out as a liquid phase polymerization in which the monomers were contacted with the catalyst composition in a liquid non-polymerizable diluent. Liquid phase polymerization is characterized in that a quantity of diluent is used which is in excess of the polymer formed.
It is common practice in the preparation of the present polymers by means of liquid phase polymerization, to use a liquid non-polymerizable diluent in which the catalyst composition dissolves but the polymers do not dissolve. During such polymerization the polymer is obtained in the form of a suspension in the diluent. After the required degree of polymerization has been achieved, the polymerization is usually terminated by cooling and releasing the pressure. The polymer is isolated from the suspension, for instance, by filtration or centrifugation. The pure diluent is recovered from the remaining liquor, for instance by distillation and can be recycled.
From some applications polymers of relatively high molecular weights are of particular value. The molecular weights of the polymers are influenced by the temperature at which the liquid phase polymerization is carried out, in that at otherwise similar reaction conditions a decrease of the reaction temperature will result in a rise in molecular weight. However, a decreased reaction temperature will be attended with two further effects. A decrease of the reaction temperature results in a decrease of the reaction rate, and a decrease of the reaction temperature will lead to a decrease of the polymer bulk density. Generally, in liquid phase polymerization a decrease of the reaction temperature to obtain only a moderate increase of the molecular weight will give rise to a considerable drop both of the reaction rate and of the bulk density of the polymers. It is desirable that the reaction rate be high and that the polymers with high bulk densities by formed.